1. Field of the Invention
The present invention relates generally to a wireless data communication network switching device used for a wireless data communication system and a wireless data communication network switching program used to implement the wireless data communication network switching device, and more specifically to a wireless data communication network switching device which can implement automatic switching of wireless data communication networks for least cost (or optimized charge) without change to any existing access router as well as to any existing client or server, and a wireless data communication network switching program used to implement the wireless data communication network switching device.
2. Description of the Related Art
Recently, in a wireless wide area network (wireless WAN) such as a mobile telephone network, data communication services employing packet-switched network technology, including the “i-mode” service available from NTT DoCoMo, Inc., have been rising in popularity.
Such a packet-switched network has an advantage that its service charge is lower than that of a circuit-switched network for small communication traffic such as a text mail. However, when the size of contents is large as is the case with a huge file attached to a mail or an image content for WWW, the circuit-switched network would have an advantage over the packet-switched network in terms of service charge.
In general, it is considered that the packet-switched network is more suitable for a small discrete communication traffic, while the circuit-switched network is more suitable for a large continuous communication traffic and thus, there is an increasing need for automatic switching of communication networks depending on a communication traffic.
For indoor use, the advent of a new communication scheme such as Bluetooth (a short-range wireless transmission technology) in addition to the conventional IEEE 802.11 standard promotes the widespread proliferation of wireless local area network (wireless LAN) systems in offices and homes and thus, there has been a drastic increase in users who adopt a wireless WAN system for outdoor use and a wireless LAN system for indoor use such as office or home use.
Such a user would feel an increasing need to have a service which can automatically switch from the chargeable wireless WAN system to the no-charge wireless LAN system when the user goes back to his/her office or home from the outdoors.
Automatic switching of prior wireless data communication networks for least cost has been usually accomplished within a single wireless data communication network such as a PHS system using an ISDN service called Always On/Dynamic ISDN (AO/DI) or a wireless data communication network using the Bandwidth Allocation Protocol/Bandwidth Allocation Control Protocol (BAP/BACP)
More specifically, as shown in FIG. 12, the automatic switching of a packet switching channel and a circuit switching channel within a single wireless data communication network has been accomplished cooperatively between a mobile computer and an access router by using the functions specific to the wireless data communication network and the functions of its link layer.
However, for numerous wireless data communication networks such as the PDC-P and PDC networks available from NTT DoCoMo, Inc., the PacketOne and cdmaOne networks available from KDDI, and the W-CDMA packet-switched and circuit-switched networks made available from NTT DoCoMo, Inc., separate packet-switched and circuit-switched networks have been actually provided.
Meanwhile, in such a wireless data communication network, as shown in FIG. 13, there have been provided access routers dedicated to the packet-switched and circuit-switched networks, respectively, and no mechanism has been provided for cooperation between these access routers.
Therefore, in accordance with the prior arts, the user may be forced to pay a higher service charge since there exists no mechanism for switching between the packet-switched and circuit-switched networks.
To solve this problem, automatic switching of different wireless data communication networks must be implemented and in addition, some mechanism must be provided for cooperation between access routers provided for these wireless data communication networks.
More specifically, since an access router provided for a packet-switched network assigns a terminal an IP address different from that assigned to the terminal by another access router provided for a circuit-switched network, switching between the packet-switched network and the circuit-switched network may cause abnormal termination of communication because the terminal may be recognized as a different one. Therefore, there is a need for mechanism to solve this problem.
However, these access routers are usually provided not only for a user's intranet but also for a carrier network or an Internet service provider (ISP) and thus, a mechanism to be provided for cooperation between them may require a considerable change to the existing infrastructure, thereby making it very expensive.
Moreover, the automatic switching adopted for the prior ISDN service AO/DI (i.e. the automatic switching of a packet switching channel and a circuit switching channel within a single wireless data communication network) is performed from the packet switching channel to the circuit switching channel when the communication traffic exceeds a predetermined value and thus, it may cause an increased service charge.
Therefore, if the communication traffic increases abruptly and then decreases, the prior system will perform the automatic switching even though it may result in a higher service charge than the case where the channels would not be switched.